Author of the month: Anthony Horowitz

When he started to climb the inside of the 150m-high crane - the height of a small block of flats - Anthony Horowitz expected to be surrounded by little footholds and handgrips every step of the way. "But all you get," he says "is an ordinary, vertical ladder going up the centre of this crane. And, of course, it's windy, so the ladder sways." He's not great with heights either, he adds. So why do it? "I think everyone should test their limits," he answers.

He stretches his by researching as thoroughly as he can the adventures of his teenage hero Alex Rider. Rider deploys a crane in Point Blanc, second in the series which has taken Horowitz from successful jobbing writer to the kind of best-sellerdom that means he needs a personal assistant to organise his speaking commitments. This week, Skeleton Key, the third Rider adventure, was awarded the Red House best children's book of the year prize - Horowitz's first award, and the only one in the country voted for entirely by children. (When JK Rowling won, she wouldn't put down the trophy, saying: "Roald Dahl held this, I'm hanging on to it.")

We are sitting in his garden - which comprises mainly grass and a trampoline for his two sons, but also a two-story office for Horowitz that is built into the terrace so cleverly it wouldn't be out of place in a James Bond movie - and talking about Alex Rider's current knife-edge struggle. No, not one in Eagle Strike, the latest instalment in Rider's life. We are discussing whether Rider makes it to the big screen, or not.

As recently as May it was a done deal. "I absolutely cannot tell you the name of the director," Horowitz says. Then, "OK, it was Christopher Columbus [director of the Harry Potters], but another boy spy came along, and I haven't heard a word since." Well, Rider has come out of far worse scrapes than this; it's just a matter of time till we hear the happy ending. So I ask Horowitz how much money he makes these days, and for about five seconds he's not going to talk about that, certainly not, it's so meaningless, until he says, laughing at himself really, "Oh, OK. Each book has sold 250,000, they sell for £5.99 and I get 10% of that - you work it out."

Except, of course, that Rider is only part of the story. Now 47, Horowitz is reaping his rewards after years of hard work as a television and film screenwriter (Foyle's War, Midsomer Murders), as well as author. He is halfway through a three-script deal with Columbia (the first one rejected, a second still being considered, and a third one not yet written.) But he came close to giving up children's writing altogether, when his early books didn't sell.

The turning point came when Horowitz wrote Granny, and moved to Walker Books. Like much of his material, it gives a completely unvarnished portrait of an adult drawn from his own background.

"I did her a favour," he says of his hated grandmother. "I made her amusing, which she certainly never was in real life."

Awful grown-ups, blown up out of proportion and so rendered comical, are a theme of his books - a product of his feelings about adults and how they damage children. Horowitz describes his parents as emotionally very distant, despite the context of a supposedly close Jewish family (after the death of his mother, he visited the reviled granny every week until she died).

Then, when Horowitz was 23, his father died, leaving the family's considerable wealth in a Swiss bank account without ever having told anyone the details - the money remains unrecovered to this day. His mother went from being a wealthy socialite to working as a secretary, aged 50, for a building company in St Albans.

"I think my writing began with my mother when I was six," Horowitz says. "She'd come in at night; she didn't read to me - she told me all the horror stories from the films. The Fly was my favourite, and all the Frankenstein and Dracula films, and The Mummy." A slightly unusual bedtime choice, I say. "Yes, she was an unusual mother." In a low corner of his office, right out of his line of vision when sitting at his desk, he keeps the birthday present his mother gave him when he was 13. It's a human skull, which she bought in a medical shop in Holborn. "It's true that I asked for it," Horowitz tells, "but it was amazing that she went out and got it."

It is his choice of the word "amazing", implying admiration and almost delight, rather than any recoil from this bizarre gift, that explains the writer he has become. If you want to invent a boy hero, be prepared to be amazed by what life throws up.

- If you are a child/have children interested in judging books for the Red House award, contact the Federation of Children's Book Groups via the website www.fcbg.org.uk